The pyroelectric detector offers several advantages over other detector materials for infrared (IR) systems applications. The room temperature operation and the inherent background subtraction are the most significant. Also, the presently used readout scheme for pyroelectric detectors is the vidicon tube, which utilized the electron beam readout. The electron beam read-out consumes power in heating a filament, requires large bandwidths since pixels are read out one at a time, introduces noise via the shot noise in the vidicon beam, and, due to the finite beam impedance, increases the RC time constant of the readout. Even with these disadvantages, the pyroelectric vidicon is a viable contender for the medium performance infrared imaging system.
An alternate readout scheme to overcome each of these disadvantages would greatly improve performance of the medium performance imaging system. Each of these disadvantages can be overcome by the solid state charge coupled device readout for a two dimensional pyroelectric detector array explained herein. A solid state readout that utilizes charge coupled device transfer means is a novel approach in that it capitalizes on each of the unique properties of the pyroelectric detector. Each detector in a two dimensional pyroelectric array is directly interfaced by interfacing means, such as DC current limiting means, to a two dimensional charge coupled device.
One of the primary advantages of coupling a pyroelectric element to the charge coupled device is the ability of the pyroelectric detector to reject background charge. Signals from a normal infrared scene are comprised primarily of background flux plus one to two percent signal. The large quantity of background flux produces currents, which quickly over fill CCD buckets. However, since the pyroelectric detector does not respond to the background flux, only the signal charge flows into the CCD. The CCD buckets do not saturate when the pyroelectric detector is coupled to the CCD readout chip.